As is known, many pourable food products, such as fruit juice, UHT (ultra-high-temperature treated) milk, wine, tomato sauce, etc., are sold in packages made of sterilized packaging material.
A typical example of this type of package is the parallelepiped-shaped package for liquid or pourable food products known as Tetra Brik Aseptic (registered trademark), which is made by folding and sealing laminated strip packaging material.
The packaging material has a multilayer structure substantially comprising a base layer for stiffness and strength, which may comprise a layer of fibrous material, e.g. paper, or mineral-filled polypropylene material, and a number of lamination layers of heat-seal plastic material, e.g. polyethylene films, covering both sides of the base layer.
In the case of aseptic packages for long-storage products, such as UHT milk, the packaging material also comprises a layer of gas-barrier material, e.g. aluminium foil or ethyl vinyl alcohol (EVOH) film, which is superimposed on a layer of heat-seal plastic material, and is in turn covered with another layer of heat-seal plastic material forming the inner face of the package eventually contacting the food product.
Packages of this sort are normally produced on fully automatic packaging machines, on which a continuous tube is formed from the web-fed packaging material; the web of packaging material is sterilized on the packaging machine, e.g. by applying a chemical sterilizing agent, such as a hydrogen peroxide solution, which, once sterilization is completed, is removed from the surfaces of the packaging material, e.g. evaporated by heating; the web of packaging material so sterilized is then maintained in a closed, sterile environment, and is folded and sealed longitudinally to form a vertical tube.
The tube is filled with the sterilized or sterile-processed food product, and is sealed and subsequently cut along equally spaced cross sections to form pillow packs, which are then folded mechanically to form respective finished, e.g. substantially parallelepiped-shaped, packages.
Alternatively, the packaging material may be cut into blanks, which are formed into packages on forming spindles, and the packages are filled with the food product and sealed. One example of this type of package is the so-called “gable-top” package known by the trade name Tetra Rex (registered trademark).
To open the packages described above, various solutions have been proposed, including reclosable opening devices made of plastic material and substantially comprising a spout, e.g. tubular, defining a through opening and fitted to a hole in a wall of the package, and a removable, e.g. screw or hinged, cap fitted to and outwardly closing the spout.
When producing the opening device, the opening of the spout is sealed by a plastic confetti portion connected integrally to the spout and detachable from it along a smaller-section annular tearable membrane; on the side facing the cap, the confetti portion has an integral projecting pull ring, the free end of which is pulled by the user to detach the confetti portion from the spout along the tearable membrane and so open the product pour opening. More specifically, the pull ring extends inside, and at a predetermined distance from, the spout.
Using the opening devices described, the package is easy to open, with a reasonable amount of effort required of the user, and the confetti portion is detached neatly from the spout.
The same does not apply, however, in the case of packages requiring not only liquid but also gas sealing where the opening device is fitted to the packaging material.
In such cases, solutions are known in which the confetti portion of the opening device is fixed directly over a prelaminated hole in the packaging material, i.e. a hole formed in the base layer only and covered by the other lamination layers, including the layer of gas-barrier material.
Using this solution, opening the package calls not only for detaching the confetti portion from the spout, but also for tearing the layer of barrier material against the edge of the hole through the base layer. With commonly used barrier materials, such as aluminium, this invariably results in an increased effort by the user to unseal the package and in a jagged, frayed edge of the hole, thus impairing smooth pour-out of the food product.
In order to solve this problem, the Applicant devised a method and apparatus, disclosed in EP-A-2008787, for injection molding the opening device directly on the prelaminated hole of the packaging material.
In practice, the molten plastic material is injected onto one side of the prelaminated hole to cover it up to an annular peripheral portion thereof and to form, in this way, a plastic confetti portion directly attached to the prelaminated hole; the molten plastic material is then forced to pierce the prelaminated hole at such annular peripheral portion to form a pouring spout of the opening device projecting from an opposite side of the prelaminated hole and attached to the confetti portion through a smaller-section annular membrane connection portion adapted to be torn by the user to open the package.
In this way, the material forming the prelaminated hole is first pierced through and then resealed by the plastic material forming the spout. Therefore, the resulting package has the necessary gas-sealing properties, while at the same time is easier to open than known packages with gas barrier.
The Applicant however observed that, during the injection operations, the prelaminated hole was not always regularly pierced on the confetti portion side, but tended to break on the spout side. This caused portions of the material of the prelaminated hole to be entrapped into the plastic material forming the tearable membrane, so making this solution not completely satisfactory as to the effort required to the user to unseal the package and the pouring quality.